This invention relates to a method and apparatus for controlling ignition in an internal combustion engine, and more particularly to a method and apparatus for controlling spark ignition in an internal combustion engine by reignition of the combustion mixture in the combustion chamber of the engine based on sensed conditions in that chamber so as to improve combustion and to reduce cycle-to-cycle variation. This invention can be employed to improve overall engine performance or to reduce or eliminate engine misfires.
Cycle-to-cycle variations in the combustion chamber are undesirable characteristics of operating and running a spark ignition engine. The causes of these combustion variations have been attributed to variations in the air/fuel mixture, motion or turbulence (especially in the vicinity of the spark plug), fuel and air charging, and fresh air and residual mixing. The results of these combustion variations are variations in work output or indicated mean effective pressure (IMEP), combustion efficiency, and emissions on a cycle-to-cycle basis. These combustion variations can manifest themselves in a variety of ways including randomly varying misfires, slow burns, partial burns and fast burns, including knock. These phenomena are generally more evident under high throttle, high exhaust gas recirculation (EGR), low speed, low turbulence, cold start and lean air/fuel ratio engine operating conditions.
It is well known that the timing of spark ignition is important in obtaining maximum or desired efficiency and proper operating characteristics of the internal combustion engine. It is also generally, understood that the resultant combustion event is a function of ignition and early flame development, and a poor combustion event is known to be primarily a function of those conditions that are present in that individual cycle.
Control of a poor individual cycle should therefore preferably be based in large part upon the characteristics of that cycle as it develops. Accordingly, the inventors have provided a method and apparatus for detecting an impending poor cycle or misfire early in the combustion cycle, and for taking corrective action in the form of reigniting that same cycle to improve the resultant burn of that cycle, to reduce overall cycle-to-cycle variations, and to mitigate the poor effects of increased exhaust emissions and fuel consumption that would otherwise result if the impending poor cycle was not corrected.
The inventors have further determined that an impending poor cycle can be detected using only a luminosity detector which detects the luminosity of gases in the combustion chamber. The resulting luminosity signal can then be employed to determine if a poor cycle should be reignited. Alternatively, the inventors have determined that only a pressure sensor or transducer which senses the pressure in the combustion chamber can be used to detect a developing poor combustion cycle, in which case the pressure signal is used as a basis for reigniting a poor cycle. In each of these cases, the measured luminosity or pressure can be compared with a desired or expected threshold value for that measured parameter. If the comparison indicates that a poor cycle or misfire is imminent, that particular cycle can be reignited. This reignition may utilize the original spark plug, an alternate plug, multiple plugs, multiple discharges or a high energy ignition system.
The setting of the threshold will affect the percentage of cycles which are reignited and will largely depend on the objectives for which this conditional reignition strategy is employed. For example, this conditional reignition strategy can be used only to eliminate misfires, or it can be used to increase the overall engine efficiency at a specific operating condition. In the case of misfire elimination, conditional reignition or spark would be needed much less frequently (perhaps only 10% or less of the cycles) than if the objective is to increase engine efficiency. In this latter case, reignition could occur up to 100% of the time depending on the specific operating conditions of the engine. Maximum engine performance under some operating conditions will require multiple sparking of every cycle, while maximum performance under other operating conditions can be achieved with less than 100% multiple sparking. The threshold can also be set independently of the engine operating condition.
A number of patents have suggested improved ignition systems and the following patents are typical:
U.S. Pat. Nos. 3,620,201; 3,898,971; 3,926,165; 4,217,872; 4,164,912; 4,341,195; 4,653,459; 4,181,112; 4,398,526; 4,428,349; 4,438,751; 4,414,954.
However, as previously noted, the inventors have determined that the reignition of a particular cycle can be based on detected conditions in the combustion chamber during that same cycle. The inventors have also determined that only an in-cylinder luminosity measurement, or alternatively, only an in-cylinder pressure measurement can be used to detect an impending misfire or a developing poor combustion cycle and as a basis for reigniting that same cycle if required
It is, therefore, a principal object of this invention to provide an improved apparatus and method for operating an internal combustion engine, wherein a luminosity detector or a pressure sensor is used to detect an impending poor cycle or misfire during that cycle, in which case that same cycle is reignited to improve combustion for that cycle. In addition, this reignition strategy can be used to improve overall engine performance or only to eliminate or reduce misfires.
It is another object of this invention to provide an improved method for operating an internal combustion engine and apparatus therefor, wherein only a luminosity detector, or alternatively, only a pressure sensor is used to detect an impending poor cycle or misfire, in which case a particular cycle is reignited to improve combustion for that particular cycle.
It is a further object of this invention to provide an improved apparatus and method for operating an internal combustion engine, wherein a particular cycle is reignited using the in-cylinder luminosity or pressure measurement to reduce the number of poor burns or misfires so as to reduce CO and unburned hydrocarbon emissions.
It is a still further object of this invention to provide an improved method and apparatus for operating an internal combustion engine which reduces the number of poor burns and misfires so as to increase work output of the engine and to improve fuel consumption.
It is yet another object of this invention to provide a method and apparatus for operating an internal combustion engine so as to reduce the number of overly fast burns by reducing the number of misfires or incomplete burns which typically precede and produce them.
It is a still further object of this invention to reduce the cycle-to-cycle variation in an internal combustion engine so as to extend the lean misfire limit, increase the EGR tolerance improve idle and cold start operation, and to permit operation of low turbulence, high volumetric efficiency, high power density engines.